Silicious material of low density.



I UNITED STATES PATENT OFFICE.

WILLIAM C. "ABSEM, OF SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SILICIOUS MATEBIAL OF LOW DENSITY.

No Drawing.

Specification of Letters Patent. Application filed June 24, 1912. Serial No. 705,382.

Patented Nov. 4, 1913.

parent density which is of especial Valueasa heat insulator although useful as well for other purposes.

When a viscous material, such' as an al-' kali silicate, containing considerable water is heated to an elevated temperature the rapid evaporation of water causes the material to swell up, or intumesce, to form a light, cellular froth having a volume anywhere from to 100 times greater than the original material; When the partially dehydrated viscous material is comminuted and the particles subjected to further heating the particles swell up to. form distinct,

frothy pellets or bubbles of very low density. In accordance with my present invention,-

the intumescent material formed in this manner is converted to a more refractory material without essentially changing its structure. For example, the alkali silicate is converted b means of an acid to silica, or by means 0- a salt to silicate more refractory than the alkali silicate without necessarily destroying the cellular structurefof the intumescent material. 7 4 y The novel features of my invention are pointed out with greater particularity in the appended claims.

According to one method of "carrying my invention into effect the intumesced'inaterial is first prepared as follows: A solution of sodium or potassium silicate, known also as water glass has its water content re-- duced by evaporation to about 15-30%, preferably to about 20%. The material is then heated to a temperature of 300-400 C. to cause it to puif up, or intumesce. I prefer to previously crush the silicate which is quite brittle when containing about 1 5430% of water. The crushed mass is sifted and segregated, the finer particles being retained and used for the intumescing process. I prefer particles retained by a sieve having 10 to meshes per square inch. The particles in this case are heated insulator.

to a temperature of 300 to.4=00 C. while being agitated to avoid sticking. The prodapparent density per given volume of .01 to.-'.O3. I do not lay claim herein to this product, the same being described and claimed in a patent issued to Walter Arthur on October 15, 1912, No. 1,041,565.

Intumesced alkali silicate either in massive or coherent form, or in the state of distinct bubbles or pufl particles, is treated according to one modi cation of my invention with'a dilute acid such as hydrochloric acid. The time required for treatment depends somewhat upon the, concentration of uct. consists of bubble-like pellets having an I the acid, and somewhat upon the tempe'rature. The treatment is continued until the material after washing contains little or no sodium. When using a. solution containin 11% HCI by weight, the treatment should be continued for about 24 hours at room temperature. the silicate, converting it into silicic acid, (SiO,+H O) andthe alkali salt of the acid which has been employed. For example, when thus treating sodium silicate there is formed silicic acid and sodium chlorid. The material is then preferably washed and dried. The silicic acid may then be converted into silica; SiO,, by firing to a temperature of 400 C. or higher. cases, the alkali salt may be left in the finished product without detriment. The product is structurally pseudomorphic of the intumesced silicate. 'In' other words, each particle of silicate has been converted in s'itu tosilicic acid and finally *to silica without substantially changin the physlcal structure of the material, as t e intumesced -water glass is but, very slightly soluble in water. The final product has a melting point of about '1650" C. and a density approximating that of the intumesced silicate. Because of this low density and cellular structure the material is a very eflicient heat Its heat capacity also is correspondingly low.

According to another modification of my invention, the intumesced silicate is treated with an acid vapor, for example, by the vapor of hydrochloric acid. After the treatment with acid vapor the material may be washed if desired, and after drying fired as above indicated.

According to still another modification of In some my invention, the intumesced silicate is treated with a solution which will-convert the same into an insolublematerial other than silicic acid. For example, it may be treated with a solution of salt of a metal forming an insoluble silicate, such as salts of aluminum, magnesium, calcium, barium, and the like. In thiscase', a double decomposition is effected with the formation of an insoluble silicate and the alkali salt of the acid radical of the compound with which the silicate is treated. For example, when an intumesced sodium silicate is treated with aluminum sulfate there is formed insoluble aluminum silicate and sodium sulfate. If desulfate may be removed this case may as well be sired the sodium by washing but in left in the material without detriment.

Other examples might be cited illustrating the general procedure of converting the frothy silicate to more refractory material. The silicate may be treated with a solution of fluosilicic acid, HSiF which will result in the formation of silicic acid and sodium physical form of the original intumesced material.

form of a cellular 4. The process which consists in heating a water-containing alkali silicate tdatmperature at which the water'is driven off with intumescence and then treating with a reagent to convert the silicate in situ to a more refractory material.

-5. The process which consists in heating a water-containing alkali silicate to a temperature at which the water is driven off with intumescence, then treating with dilute hydrochloric acid to convert the silicate into silicic acid having the physical form of the particles of the silicate thus treated, and finally. heating to convert the silicic acid into silica. 4

6. The process which consists in treating an intumesced alkali silicate with an acid to decompose the silicate and convert the same to silicic acid, having the general form of theintumescent silicate, and then heating to convert the silicic acid into silica.

7. A heat insulating material consisting at least in part of silica and comprising pellets of low density having a structure pseudomorphioof intumesced silicate of an alkali metal.

,8. The process of making refractory heatinsulatinmaterial which consists in heating pellets of alkali silicate to about 300 to 400 C. to intumesce the same, treating with dilute acid to convert thesilicate-to silicic acid having a structure similar to the silicate, and finally converting the silicic acid to silica.

In witness whereof, I have hereunto set my hand this 22nd day of June 1912.

, WILLIAM J. ARSEM.

Witnesses:

MARY E. CHRISTIE, HELEN ORFORD. 

